This invention relates to electronic chimes and, more particularly, to improvements in chimes including electronic circuit for producing signalling chime sound of at least two different and sequential sounds upon actuation of calling push button.
Various circuits have been already suggested for electronic chimes. For example, such circuit as shown in FIG. 1 has been used, in which a current source A' is connected through a calling push button PB with an electronic signalling circuit ES for producing audible frequency signals of at least the two sounds, and a speaker SP' is connected to the circuit ES so that the speaker will be sounded by an ON-signal of the calling push button but, in the case of electronic chimes of which signalling chime sound has a fixed cycle, there is a defect that a time point in the cycle at which the chime sound stops cannot be fixed. FIGS. 2 and 3 show frequency wave forms gradually attenuated of a chime sound that has a fixed cycle. In case the sound stops, as in FIG. 2, after the completion of such fixed cycle of the chime sound consisting of a high sound HS and a low sound LS, the sound will become natural but, in case the push button is switched on at a time t.sub.1 and is switched off at a time t.sub.2 intermediate the low sound period, the low sound will be interrupted on the way as shown in FIG. 3 and the sound will become unpleasant or somewhat unnoticeable.
Also, such an electronic signalling circuit as is shown in FIG. 4 has been conventionally used. In this circuit, condensers C.sub.1 and C.sub.2 of an oscillating circuit and condensers C.sub.3 and C.sub.4 of an attenuating circuit are included so that two different sounds will be generated respectively at ON and OFF strokes of the push button PB so as to be gradually attenuated. In this case, too, there are defects that, as these condensers are connected as external parts of a semiconductor integrated circuit, the number of their connecting pins increases, there is no effect on the manufacture and use of the semiconductor integrated circuit; that, as the condenser C.sub.3 must be charged during the waiting time when the push button PB is opened and its discharge current must be consumed, it is necessary to always impress a current source voltage Vcc on the circuit, there is an electric power consumption when the circuit is not used, the arrangement is therefore not adapted to the use of a battery power source; that the sounds consist of two sounds utilizing the charge and discharge of the condensers at the time of switching on and off of the calling push button PB and, in order to obtain a chime sound consisting of more than two different sounds, there must be separately provided a circuit consisting of a contact repeatedly switched on and off or a switching transistor and an oscillator and so on so as to render the circuit complicated and bulky. The present invention has been suggested to remove such defects as above.